Low interference controlled switching circuit for multiple loads

Abstract

A power control circuit for at least two ohmic loads includes power semiconductors, switching elements and a control unit for adjusting the power consumption of the loads. In order to comply with international standards to avoid disturbances in mains supply systems when higher loads are switched, a simple and cheap circuit is described which is also suitable for smaller domestic appliances such as light cookers, flat-irons, cooking vessels etc. A control unit controls a switchable power semiconductor unit which can pass current in two directions and connects one or both loads to the single power semiconductor unit via the switching elements in a variety of circuit configurations so as to adjust the power to the loads as required.

We claim: 
     
       1. A circuit for controlling power to at least two loads from a source of AC supply voltage comprising: a bidirectional power semiconductor unit, switching elements, and a control unit for controlling operation of the power semiconductor unit and the switching elements so as to control the power consumption of the loads, characterized in that the control unit is adapted to control the power semiconductor unit and the switching elements so as to connect one or both loads to the power semiconductor unit via the switching elements in at least two power supply modes of operation. 
     
     
       2. A circuit as claimed in claim 1, wherein the power semiconductor unit has a first terminal connected to a reference potential and a second terminal connected to one load and, via at least one of the switching elements, to the other load. 
     
     
       3. A circuit as claimed in claim 2, wherein the power semiconductor unit comprises one triac or two oppositely poled thyristors and the switching elements comprise a single relay having a first and a second change-over switch. 
     
     
       4. A circuit as claimed in claim 3, wherein in a first position of the relay the power semiconductor unit is connected to a phase terminal of the AC supply voltage via the one load, a connecting line, the second change-over switch and the other load, and in a second position of the relay the power semiconductor unit is connected to the phase terminal via the one load and the first change-over switch and the other load is connected in parallel with the power semiconductor unit, the first load and the first change-over switch. 
     
     
       5. A circuit as claimed in claim 3, wherein in a first position of the relay the power semiconductor unit is connected to a phase terminal of the AC supply voltage via the one load, a connecting line, the second change-over switch and the other load, and in a second position of the relay the power semiconductor unit is connected to the phase terminal via the one load and the first change-over switch and the other load is connected in parallel with the first load and the first change-over switch via the second change-over switch and a connection line. 
     
     
       6. A circuit as claimed in claim 3 comprising a single power semiconductor unit, and a thermistor connected in a connection line between an operating contact of the first change-over switch and a rest contact of the second change-over switch in order to limit turn-on transients. 
     
     
       7. A circuit as claimed in claim 1, wherein the switching elements comprise a relay with two change-over switches for coupling the loads in series or in parallel depending on the control unit, and the power semiconductor unit includes first and second parts, one part for each switching direction, the first and second parts being associated with respective ones of the loads, each part of the power semiconductor unit, in the case of parallel operation of the two loads, having one terminal connected to a reference potential and comprising an oppositely poled diode and a thyristor. 
     
     
       8. A circuit as claimed in claim 1, wherein the switching elements comprise a relay with two change-over switches for coupling the loads in series or in parallel depending on the control unit, and the power semiconductor unit has a first terminal connected to a phase terminal of the AC supply voltage and comprises one triac or two oppositely poled thyristors. 
     
     
       9. A circuit as claimed in claims 1, 2 or 3 wherein the control unit comprises a logic device in the form of a microprocessor and, for a quasi reaction-free control of the power consumption of the loads, is adapted to control one or more of the following switching states: a) parallel operation of the two loads to the supply voltage,   b) operation of only one load with the supply voltage,   c) operation of the one load with the supply voltage and operation of the other load in a 2/3, 1/3 or 1/5 phase mode,   d) operation as under c) with pulsed phases,   e) series operation of the two loads to the supply voltage,   f) operation of the two loads in series in the 2/3, 1/3 or 1/5 phase mode,   g) operation as under f) with pulsed phases,   h) operation with both loads "off",   i) operation of the one load with the supply voltage and delayed connection of the other load with operation thereof in the 1/3 and 2/3 phase mode, and   j) operation of both loads in the 2/3 or 1/3 phase mode.   
     
     
       10. A circuit as claimed in claim 9, wherein, in a starting/turn-on cycle, the control unit causes the switching states f), e) and a), i) or j) to be traversed successively to attain the maximum power, and at least one of the switching states b) to j) is traversed to reduce the power consumption. 
     
     
       11. A circuit for controlling the supply of power to at least first and second loads from a source of AC supply voltage comprising: first and second input terminals for connection to the source of AC supply voltage,   a bi-directional controlled semiconductor switching unit,   switching means having first and second change-over switches,   wherein the switching means and the controlled semiconductor switching unit each have a control input for receiving control signals that selectively operate the switching means and the controlled semiconductor switching unit so as to connect one or both of the loads to the controlled semiconductor switching unit via the change-over switches of the switching means thereby to produce a plurality of power operating states for the first and second loads.   
     
     
       12. A power supply circuit as claimed in claim 11 wherein the controlled semiconductor switching unit has a first main terminal connected to a point of reference potential and a second main terminal connected to the first load and via one of the change-over switches to the second load. 
     
     
       13. A power supply circuit as claimed in claims 11 or 12 wherein said control signals are operative to control the switching means and the controlled semiconductor switching unit so as to selectively produce one or more of the following power operating states: a) connection of the first and second loads in parallel to the first and second input terminals,   b) connection of only one load to the first and second input terminals,   c) connection of one load to the first and second input terminals and operation of the controlled semiconductor switching unit so as to supply power to the other load from the first and second input terminals in a 2/3, a 1/3 or 1/5 phase mode,   d) operation as in state c) above but with pulsed voltages for the other load,   e) connection of the first and second loads in series to the first and second input terminals,   f) connection of the first and second loads in series to the first and second input terminals and operation of the controlled semiconductor switching unit so as to supply power to the first and second loads from the first and second input terminals in a 2/3, a 1/3 or a 1/5 phase mode,   g) operation as in state f) above but with pulsed voltages for the first and second loads,   h) disconnection of both loads from the first and second input terminals,   i) connection of one load to the first and second input terminals and a delayed connection of the other load to the first and second input terminals via operation of the controlled semiconductor switching unit,   j) connection of both loads to the first and second input terminals and operation thereof via the controlled semiconductor switching unit in the 2/3 or 1/3 phase mode.   
     
     
       14. A power supply circuit as claimed in claims 11 or 12 wherein a start-up/turn-on cycle comprises: connection of the first and second loads in series to the first and second input terminals and operation of the controlled semiconductor switching unit so as to supply power to the first and second loads from the first and second input terminals in a 2/3, 1/3 or a 1/5 phase mode, and then   connection of the first and second loads in series to the first and second input terminals, and then   connection of the first and second loads in parallel to the first and second input terminals.   
     
     
       15. A power supply circuit as claimed in claims 11 or 12 wherein a start-up/turn-on cycle comprises: connection of one load to the first and second input terminals and a delayed connection of the other load to the first and second input terminals via operation of the controlled semiconductor switching unit, and then   connection of both loads to the first and second input terminals and operation thereof via the controlled semiconductor switching unit in the 2/3 or 1/3 phase mode.   
     
     
       16. A power supply circuit as claimed in claim 14 wherein at least one of the power operating states b) to j) in claim 13 is included in the start-up/turn-on cycle. 
     
     
       17. A power supply circuit as claimed in claim 15 wherein at least one of the power operating states b) to j) in claim 13 is included in the start-up/turn-on cycle. 
     
     
       18. A power supply circuit as claimed in claim 11 wherein the switching means is controlled into a first state in which the controlled semiconductor switching unit, the second load and the second change-over switch are connected in series to the first and second input terminals, and in a second state of the switching means, the controlled semiconductor switching unit is connected in series with the first load and the first change-over switch to the first and second input terminals and the second load is connected to the first and second input terminals via the second change-over switch. 
     
     
       19. A power supply circuit as claimed in claim 11 wherein the switching means is controlled into a first state in which the controlled semiconductor switching unit, the first load, the second change-over switch and the second load are connected in series to the first and second input terminals, and in a second state of the switching means, the controlled semiconductor switching unit is connected in series with the first load and the first change-over switch to the first and second input terminals and the second load is connected to the first and second input terminals via the second change-over switch and the controlled semiconductor switching unit.